1. Field of the Invention
The invention relates to sheet-steel wheels including a disc and a rim with a mounting groove which are joined under the mounting groove, and relates more particularly to the profile of the section of the rims of such wheels.
2. The Related Art
The wheels of vehicles are subjected to repeated stresses in operation which may lead to degredation through fatigue. To measure the fatigue strength of the wheels, they are subjected to endurance tests on vehicles or on machines. The test machines reproduce in a simplified and accelerated manner the stresses of the wheels in actual use. The stresses of the wheels depend principally on the load of the vehicle for which the wheels are intended.
Standard sheet-steel wheel rims are produced by a series of operations for shaping a hoop of constant thickness. These rims thus have a substantially constant thickness. The zones of fatigue degradation of such wheels are usually located at the radii of the groove bottom, at the joining weld and at the valve hole (see FIG. 1).
The thickness of the original sheet-metal blanks intended for the manufacture of the rims is thus a function of the stresses to which the wheels are subjected in operation.
U.S. Pat. No. 5,579,578 (the disclosure of which is hereby incorporated by reference for all purposes) describes a method of manufacturing a wheel rim including one or more reverse cylindrical flow-turning operations in order to obtain a rim profile of variable thickness and, thereby, to reduce the weight of the rim. This patent gives no information about the profiles of the sections of the rims to be obtained.